This invention relates to improvements in an apparatus for driving a power seat in automotive vehicles or the like.
As shown in FIG. 1, a common mechanism for applying power to a seat of an automotive vehicle to move the seat comprises a motor 2 fixedly secured to a lower bracket 1 on the vehicle body, a power seat drive apparatus 3 fixedly secured to the lower bracket 1, a screw rod 4 coupled to the drive apparatus 3, and a nut member 6 fixedly secured to an upper bracket 5 slidably engaged with the lower bracket 1 and supporting a seat cushion. Turning the screw rod 4 causes the nut member 6 to slide along the screw rod 4, thereby moving the upper bracket 5 back and forth relative to the lower bracket 1.
A prior-art example of the drive apparatus 3 used in the above-described mechanism is illustrated in FIG. 2. The drive apparatus 3 includes a worm 8 fixedly secured to the output shaft of the motor 2, a worm wheel 7 threadedly engaged with the worm 8, a housing 9 having a bore 10, and a plug 11 fitted in the bore 10 and having a groove 12 formed in one end thereof. One end portion of the worm 8 is supported in the bore 10 of housing 9, and the other end of the worm 8 is supported by the plug 11. A screw 13 threadedly engaged with the housing 9 has an end portion of enlarged diameter received in the groove 12, thereby retaining the plug 11 in the bore 10 of housing 9. A damper 14 consisting of e.g. polyurethane is disposed in the bore 10 in abutting contact with one side of the plug 11. The opening of the housing 9 is covered by a cover 15.
The worm wheel 7 and worm 8 are aligned by turning the screw 13 so that the plug 11 supporting one end of the worm 8 will move relative to the housing 9. It should be noted that the end of the worm 8 is coupled to the motor 2 (FIG. 1) so that the rotational torque of the motor 2 is transmitted to the screw rod 4 through the worm wheel 7 and worm 8.
The alignment of the worm wheel 7 and worm 8 is extremely important for the sake of preventing the occurrence of noise during the operation of the power seat. After the drive apparatus 3 is assembled, the alignment is performed by turning the screw 13 to move the plug 11 up and down in the bore 10 of the housing 9. With the conventional arrangement, however, the plug 11 does not slide well on the damper 14 so that moving the plug 11 causes the damper 14 to drag behind it. When the damper 14 returns to its original state during operation of the power seat, therefore, the relationship between the central axes of the worm wheel 7 and worm 8 undergoes a shift and an abnormal noise is produced.